Photoconductive screen deriving light thorugh light conductor from tube filament

ABSTRACT

A television camera tube of the Vidicon type in which a photoconductive screen at one end of an evacuated envelope receives an image of a scene to be televised and is scanned by an electron beam. An auxiliary light source is provided for uniformly illuminating the screen and a light conductor, at least partly outside the path of illumination from the scene, conducts light from the auxiliary source to the screen.

J'QUY JQJ. D11 1 1 SEARCH R0 KR 396253101176 OM United State I 1 13,628,076

1 STITUTE F0. 1111251. 1e "1 [72] Inventors Willem Paul Wellland; [50]Fleld 01' Search 3 l 3/65, 65

Hans Georg Gerlach; Antonlus Joannes A Marla Van Den Bald; Louls MnartenSwart,

all 01 Emmaslngel, Elndhoven. Netherlands I 56] Reterences Cmd [21 1Appl. No. 885,914 UNITED STATES PATENTS 1 1 Filed -1 2,131,185 9/1938Knoll 3l3/65X Palemed 14, 1971 2,915,659 12/1959 Goodman 3 l 3/65 1Assign 1 Corporation 3,002,101 9/l96l Anderson et a1... 313/65 x NCWYork. 3,048,728 8/1962 Beurle 313/65 [32] Priority Dec. 24, 1968 [33}Netherlands Primary Exammer- Robert Segal Anorney- Frank R. TrifanABSTRACT: A television camera tube of the Vidicon type in which aphotoconductive screen at one end of an evacuated envelope receives animage of a scene to be televised and is [5 1 1 PHO'IO'CONDUCTIVE SCREENDERIVING LIGHT THROUGH LIGHT CONDUCTOR FROM TUBE FILAMENT 4 cmml'sDrawing Figs; scanned by en electron beam An auxihury light source 15provlded for uniformly illuminating the screen and a light conduc- [52]U.S.C| 313/65 A, I of a[ least partly outside the Path Of illuminationfrom 1116 1 250/227 313/65 LF scene. conducts light from the auxiliarysource to the screen. 1511 lm. c1 .1101] 31/28. HOlj 3l/38,HOlj 5/16Patented "Dec. 14,1971 j 3,628,076

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INVENTORs; WILLEM P. WEIJLAND HANS G. GERLACH ANTONIUS J.M VAN DEN BELOBY 1 ou1s 11151111111111 AGENT Patented Qec. 14, 1971 T 3,628,016

2 Sheets-Sheet? AND FEW: IJ L A u fufh'Wkocu new By LOUJ M. swunNVENTORS PHOTOCONDUCI'IVE SCREEN DERIVING ucrrr morwcrr ucrrr cormuc'ronFROM runs mm The invention relates to a camera tube of the vidicon typecomprising a photoconductive screen, the invention relates in particularto a Pluiiibicon.

in such a camera tube the drawback is experienced that, in the case oflow-luminosity pictures, inertia phenomena may occur as a result of thehigh resistance of the photoconductive layer of the screen in the caseof such low luminosity exposures. These inertial phenomena can bereduced by ensuring that also in case no light of a picture is incidentthe screen parties a given :quiescent current, the so-called darkcurrent. This dark current can be controlled by providing a givenuniform auxiliary illumination or background illumination of the screen.This could be done by incorporating a weak light source in the camera inwhich the tube is provided. However, in this case it is necessary toprovide elements in the optical path of the tube, which may give rise todisturbances and light reflections, particularly in color cameras inwhich the optic are very critical. Moreover, in that case, one is notfree in the choice of the color of the auxiliary light-source.

A considerable improvement is obtained if the tube according to theinvention comprises one or more light-conductive members which conductlight from an auxiliary light source in the direction of thephotoconductive screen. The auxiliary light source may be the filamentof the cathode of the tube itself but a larger control range of the darkcurrent can be obtained by the light of a separate light source, ifdesirable in combination with color filters. By conducting additionallight to the photoconductive screen, while using a light conductor, thisauxiliary light can be transferred, for example, to the collector spaceof the tube and from there distributed uniformly over the photoconductive screen by diffuse reflection.

As is known per se, the light conductor may consist of a glass rod whichis suitably bent so that the light of a light source situated in frontof one end of the rod emanates at the other end from the rod. lfdesirable the light-conductor may be formed entirely or partly bythewall of the envelope of the tube itself.

The invention will be described with reference to the accompanyingdrawing, in which:

F I68. I, 2, Band 4 are diagrammatic longitudinal cross-secthe lightguided to the screen 9 can be obtained within certain limits by varyingthe filament current 7. However, one is restricted to the minimumoperating temperature of the cathode, while the maximum adjustabletemperature may not reduce the lifetime too strongly. The limits withinwhich the background light can be controlled therefore are comparativelynarrow.

A larger control range is obtained in the embodiment shown in H68. 2 and3.

In FIG. 2 the light conductor in bent at one end in such manner thatsaid end can be passed out through the aperture of the exhaust tube inthe bottom of the tube, and be sealed in the tip of the exhaust tube.The tip of the exhaust tube is surrounded by a sheath 13 in which alight source 14 is situated. The sheath 13 may be housed in the holder 5of the tube. it is alternatively possible to bend the end of the lightconductor tioiial views of vidicon tubes according to the inventionemploying light conductors having various shapes.

HO. 5 is across-section view of a light conductor.

Reference numeral 1 in the drawings denotes the cylindrical glass wallof a television camera tube which is closed at one end by a glass windowportion 2 and at the other end by a botminosity of a picture projectedon the screen 9 through the window 2, it is desirable to provide a lowuniform background illumination of the screen 9.

As is shown in FIG. 1, this is done by means of arogll shagedr lightcondugtor 10 which is bent at one end in such manner msra' an of firefih irradiated by the filament 7 is guided through the light conductor 10to the collector space 11 inside the last electrode 12 of the electronlens of the tube and emerges there from the light-conductor. The cathodeis optically open at its lower side, so as to permit the filament lightto emanate. 'Ihe light-conductor 10 can be supported by electrodes ofthe tube bymeans of clamping members 18, 19. The electrode 12 comprisesan inner wall which is proccssed so that the light is reflected in adiffuse manner and is unifonnly distributed over the photoconductivescreen 9. The control of 21 towards the inside of the sidewall of theenvelope of the tube and to place a light source 20 at that area on theoutside. The end of the light-conductor need not touch the sidewall (seeFIG. 2). If desirable, a color filter can be arranged between the lightsource 14 and the photoconductive screen. The color filter can beprovided between the light source and the end of the light conductor, ornear the end of the light conductor. If desirable, the light conductoritself may consist of colored material. if the end of a rod-shaped lightconductor ends opposite to the sidewall of the tube, the sidewall of theenvelope may be manufactured from colored glass or a color filter may beprovided on the wall. Naturally, the color filter may also be providedon the envelope of the light source itself.

It is alternatively possible to give the light conductor a straightconstruction and seal it in the bottom of the tube, preferably by means'of a plastic material or a readily melting type of glass 15. Leadingthrough can take place at the area of an omitted contact pin. In thiscase also a sheath 13 having a light source 14 may be provided in theholder 5 of the tube (HS. 3). in order to obtain a more uniformillumination of the screen 9, two light conductor are preferably used.

In the embodiment shown in FlG. 4, again the light irradiated by thefilament of the cathode is used. By rounding off the edges of the bottom3 of the tube, and in particular of the window portion 2, and bycovering the rounded-offedges with the external readily reflectinglayer, for example, a layer of silver 16 and 17 respectively, it can beachieved that the light rays which have reached the bottom of the tubeare conveyed through the wall 1 of the tube to the window 2 andimpingeupon the photoconductive screen 9 inv a uniformly distributed manner.The radius of the rounding off of the window portion is preferably equalto the thickness of the glass of the window portion. The layer of silverl 6 may be connected to a screening means while the layer of silver 17may serve as an electric current supply member for the screen 9.Thislatter embodiment has the advantage that the construction of theelectrodes can remain the same. Light conductors are known per so.instead of a single glass rod, the light conductor may also consist of abundle of glass wires 22 which extend parallel and are adhered together.

it will be obvious that the invention is not restricted to the examplesdescribed and that many variations are possible to those skilled in theart without departing from the scope of this invention. For example, thelighbconductor may be formed differently within the scope of thisinvention. Alternatively,

several embodiments may be combined.

What is claimed is:

l. A television camera tube comprising an evacuated envelope having atransparent wall portion, a photoconductive screen having one surfacefacing said transparent wall portion for receiving an image of a scene,means to scan the opposite side of said screen with an electron beamthereby generating an electrical current corresponding to lightvariations in said scene, said scan means including an electron gun forgenerating an electron beam remote from the screen and means to deflectthe electron beam before it impinges on the screen, means for uniformlyilluminating said screen including a filaatone end.

3. A camera tube as claimed in claim 1 wherein the lightconductorcomprises a bundle of parallel glass wires which are adhered together.

4. A camera tube as claimed in claim 1 wherein the envelope wall is thelight conductor and at least the edges of the transparent wall portionare rounded ofi and are covered with a light reflecting layer so thatlight of the filament of the cathode is guided to the photoconductivescreen through the envelope wall.

l i i i. l-

UNHED STATES PATENT @FFKQE @ERTHFECATE @i CRRETYLN batent NO. 3,628,076Dated Decexfiber 14, 1971 inventor(s) W.P. Weij land; H.G. Gerlach;A.J.M. Van Den Beld ET AL It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 58 after "together" insert --as shown in Fig. 5

Signed and sealed this 19th day of December 1972.

(SEAL) Attest:

EDWARD MELETCHERJR; ROBERT G-OTTSCI-IALK Attesting Officer- 1Commissioner of Patents

1. A television camera tube comprising an evacuated envelope having atransparent wall portion, a photoconductive screen having one surfacefacing said transparent wall portion for receiving an image of a scene,means to scan the opposite side of said screen with an electron beamthereby generating an electrical current corresponding to lightvariations in said scene, said scan means including an electron gun forgenerating an electron beam remote from the screen and means to deflectthe electron beam before it impinges on the screen, means for uniformlyilluminating said screen including a filament and at least one lightconductor for conducting light by multiple internal reflection fromfilament to a point opposite the side of the screen struck by theelectron beam for providing bias illumination over substantially theentire surface of the screen struck by the electron beam, at least aportion of said light conductor lying outside the path of illuminationfrom the scene.
 2. A camera tube as claimed in claim 1 wherein the lightconductor is shaped as a rod and is bent towards the filament at oneend.
 3. A camera tube as claimed in claim 1 wherein the light-conductorcomprises a bundle of parallel glass wires which are adhered together.4. A camera tube as claimed in claim 1 wherein the envelope wall is thelight conductor and at least the edges of the transparent wall portionare rounded off and are covered with a light reflecting layer so thatlight of the filament of the cathode is guided to the photoconductivescreen through the envelope wall.